1. Field of the Invention
The present invention relates to an improved fluid catalytic cracker process and apparatus, and more particularly, but not by way of limitation, to apparatus for carrying out petroleum catalytic cracking processes and other similar processes including shutoff valves having improved valve stem guide apparatus.
2. Description of the Prior Art
Many various types and kinds of valves have been developed for a variety of applications. In the petroleum, chemical and other similar industries, fluid flow control valves operated by hand or by pneumatic, electric or hydraulic operators are commonly used. In many instances such valves are closed or opened only on occasions such as during an emergency or during the start-up or shut-down of associated equipment. For example, in petroleum refineries, slide valves and gate valves are commonly used in conduits leading fluid at high pressures and temperatures between vessels, reactors and other units. These valves remain open during normal operations and are closed only when an emergency arises or when other shut-downs occur. Often, such valves continuously remain in the open position for extremely long periods of time.
Heretofore, valve stem seizure problems have been encountered with valves in the above-described service, particularly those through which fluids and solid materials at high temperatures and/or pressures flow for long periods of time. These problems are primarily due to the pressurized fluids and solid materials entering the valve stem packing gland area and other areas of close clearance between the valve stem and valve body. After entering such close clearance areas, the materials solidify or degrade or cause corrosion of the valve stem, bringing about valve stem seizure when the valve is attempted to be closed. Since many such valves are operated by automatic operators activated by emergency shut-down devices, failure of such valves due to valve stem seizure is extremely hazardous to the safety of equipment and personnel.
A particular problem is encountered in petroleum catalytic cracking processes and apparatus of the fluidized catalyst type. The apparatus must include shutoff valves through which hot regenerated catalyst or mixtures of hot oil and unregenerated catalyst flow. The shutoff valves are in addition to flow control valves which are used to control process variables, and are used only during emergency or normal shut-down and start-up procedures. Consequently, such shutoff valves often remain in the fully open position for long periods of time during which portions of the catalyst or catalyst-oil mixtures flowing through the valves at high temperatures find their way into areas of close clearance between the valve stem and the valve body, i.e., the valve bonnet and valve stem packing gland areas. Because these areas of the valve are relatively cooler than the hot catalyst-oil materials flowing through the valve, the materials in the cooler areas solidify into a cement-like substance which causes the valve stem to become immovable. Also, shutoff valves through which catalyst particles flow with or without oil in admixture therewith often become immobile due to the abrasive catalyst entering areas of close clearance between the valve stem and valve body causing the valve stem to stick due to abrasion and galling.
By the present invention an improved valve stem guide apparatus is provided particularly suitable for use in slide, gate and other valves utilized in apparatus for carrying out fluid catalytic cracking processes as well as other processes, which apparatus prevents pressurized fluids and materials passing through the valve body from flowing through the guide apparatus into areas of close clearance between the valve stem and valve body.